Answer:
a) 30.24 m
Explanation:
The particle s a lifetime of 112 ns and travelled at 0.9c from the point of view of observer A.
0.9c = 2.7e8 m/s
112 ns = 1.12e-7 s
Since we have the time and the speed from the point of view of observer A, we can use those to calculate the distance from the point of view of observer A without any transformations
[tex]d = v * t = 2.7e8 * 1.12e-7 = 30.24 m[/tex]
From the point of view of observer B, the particle will be at rest and the lab will be moving at 0.9c. The travel between the marker will take 280 ns from the point of view of observer B.
Therefore the distance from the point of view of observer B will be:
d = 2.7e8 * 2.8e-7 = 75.6 m
Now, there is an error here, because observer A should see the particle as having a longer life than as observer B sees it and the distance observer B sees should be shorter, I suspect a typo in the question.